Without limiting the scope of the invention, its background is described in connection with characteristics of various adhesives.
Acrylic-based adhesives have been used in applications that require compositions exhibiting fast curing and flexible adhesive qualities. While acrylic-based adhesives are generally good for causing adhesion to difficult substrates such as plastics, they often have undesirable heat resistance. Curable epoxy resins have also been used as adhesive compositions. Epoxy adhesives form a tight polymer network and generally exhibit desirable thermal properties. Epoxy adhesives, however, tend not to bond to plastics well and tend to be brittle and exhibit poor impact strength. Generally, epoxies are slow curing which renders them inappropriate for many industrial applications.
Many adhesives exhibit poor physical properties such as decreased impact strength, poor adhesive bonding capabilities, and setting times, depending on the application. Adding impact modifiers and other copolymers to the adhesive may improve these physical characteristics. Unfortunately, while impact modifiers tend to improve some physical properties, they typically exhibit poor heat resistance. With the use of more and more plastics in industrial applications such as for example, automobile assembly, there is a continuing need for adhesives that can be used on plastics as well as metals to form adhesive bonds that will hold up under a wide variety of adverse conditions.